I have a theory of evolution which I have been working on. It is a form of sexual selection which I call "proliferation and precipitation". It is designed to explain the continuing and accelerating evolution of humans.

Human population has proliferated - there are more than six billion of us and many of us have a great range of freedom in terms of movement. This means that each human has a broad pool from which to select a mate. I submit that this precipitates evolution towards certain ends.

One example I use is obesity. Assume that obese people are less likely to successfully procreate for one reason or another. For the sake of argument, imagine that an obese person is 15% less likely to procreate than a physically healthy person. That means, over time, whatever genetic influences cause/allow obesity will be reduced. It's not so much "survival of the fittest" as it is "culling of the weakest". The same can be seen in nature. Only the weakest herd members are killed by the wolves. The rest of the herd members have a decent chance at procreation. The same can be said of humans. Most of us have the opportunity to have children, so "survival of the fittest" no longer applies.

Now, there are many factors which go into sexual selection. Many people value different things in a mate. Some people place physical fitness very high. Other people value intelligence or assertiveness.

The most controversial aspect of my theory suggests that a certain amount of stratification or grouping will occur. People in certain socioeconomic segments tend to value specific traits. Highly educated and intelligent individuals tend to value intelligence. Therefore, it is possible that those traits will become concentrated within that social bracket. This is only one form of what I call "precipitation".

Consider people who are always very skinny, no matter what they eat or how much they exercise. In today's society, this is an intrinsic advantage. While impulse control can play a big part in physical health, some people seem to not need any impulse control, and yet they stay healthy. As I mentioned before, most people have a chance to have children. That means those skinny people will likely pass on their advantage to their children. Over time, those advantageous traits should permeate much of the gene pool. At the same time, the obesity rate should continue to decline.

It seems that social values can precipitate adaptation. Obesity rates in America have stopped climbing. Researchers believe this is because "all who are susceptible to obesity have become obese". Now that the cap has been reached, and each obese person might be less likely to procreate, that trait should start to become more and more rare. Susceptibility to obesity is an intrinsic disadvantage.

Furthermore, the great number of people on earth allows for tremendous variation to exist at any given time. Greater variation coupled with greater range of selection should power ever accelerating human evolution.

As an example; consider two highly intelligent individuals. Both of them value intelligence and so they are attracted to each other. Theoretically, since intelligence is a common factor, whatever genes responsible for their individual intelligence should be passed on and concentrated in their offspring. Their children should be more intrinsically intelligent than either parent. To date, only a small handful of genes have been linked to intelligence, but that establishes a precedent. Perhaps one parent has 3 gene variations which have been identified as affecting intelligence, while the other parent has 3 separate genes similarly identified. It is possible that one of their children could have all 6 genes, and thus the trait of intrinsic intelligence should be greater.

Lastly, I'd like to indicate how this could be bad for some individuals. Psychology studies have shown that people are typically attracted to similar people. This means that negative traits such as poor impulse control and susceptibility to obesity could just as easily become concentrated as traits such as intelligence and physical fitness. This is what I mean by "genetic stratification".

Addendum: I have remembered one distinct story about how such a thing could benefit humanity. There is a small island off the coast of New England which has a peculiar population of opossum. The opossum of that island live much longer than their mainland relatives. This is in part due to lack of predation on the island. However, even opossum from the mainland do not live so long even without predation. This is because, over time, the opossum on the island who lived to reproduce longer passed on more children. In a sense, it was lack of selection and pressure that allowed the island variety to live longer. A few hardy opossum had many more offspring than the average opossum, and that pattern has repeated itself over the 300 or so years that the island population has been isolated. While the possums represent physical segmentation, it is not a far stretch to say that some segments of society do not intermix all that much. It is not total isolation and there are always exceptions.

I think you'll find that sexual selection traits in humans are not that malleable - there are basic universals, well-supported by studies.

Other features vary not just between cultures but within cultures. There are too many necessary roles within human colonies for traits to be good or bad. Intelligence is not always an advantage, for instance.

And obesity is memetic, for the most part, and would follow a Lamarckian pattern.

I have spent much time considering the argument that "obesity is mostly memetic"

1) The memetic part of obesity is modern agriculture.

2) The genetic aspect of this, however, is a propensity to become obese. Some people simply have less of a tendency to become obese, regardless of what they eat. These people have the intrinsic advantages of which I speak.

So, in effect, our memes are driving further evolution in humans.

Humans have only recently conquered famine (and only in the most developed parts of the world). Humans are still genetically equipped to deal with famine through storing extra fat. In the most modernized areas of the world, this is not necessary. Plenty of evolutionary studies have proven the "use it or lose it" concept (think tails). Since humans no longer need famine resistance, those traits should start to be eliminated. By simply eliminating famine resistance as selective trait, obesity should eliminate itself.

The fact that there are so many humans, and therefore more random variation, means that this process should be much faster than classical evolutionary models. When selective pressures are high enough, evolutionary processes accelerate (see polar bears). Humans were at equilibrium prior to the industrial revolution. However, as pointed out, memetic interference has pushed the species out of equilibrium. Another interfering meme is medicine. Relatively unhealthy people can now procreate, meaning sexual selection is the only remaining force driving evolution.

People tend to be attracted to people who are a good genetic match. This is achieved through many methods. Given the high population and physical mobility and large variation, that should allow the precipitation of faster evolution. In the case of obesity, I expect two distinct changes to be identified in the next few decades; loss of famine resistance as well as metabolic regulation changes. In essence, human bodies will adapt to keep only what they need, no matter what is eaten or how much.

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PS - in terms of suicide rates among any particular bracket - it is the wealthiest people, regardless of career. The top wealthiest people are the most likely to commit suicide. Fortunately, this is relatively small segment of the population.

@Darby - I think you meant to imply "sexual attraction" - but it is not so simple as a few well studied traits. Physical attraction, chemical attraction - these are only the objectively studied aspects. Cultural and memetic factors are also extremely important. What type of person are you? What do you do with your life? What habits do you have? These are psychological aspects which are only now really being studied.